This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 9900897-1 filed in Sweden on Mar. 12, 1999; the entire content of which is hereby incorporated by reference.
The present invention relates to a packet data communication system which is connected to a telecommunication system and to another packet data communication system, and which gives transmission priority with respect to short delays for information packets received from the telecommunication network.
In packet data transmission systems, the channels through the network share the capacity of the links within the system. This is in contrast to circuit switched communication systems where a corresponding link is dedicated to each transaction. The traffic generated in packet data systems is in the nature of bursts, i.e. traffic load varies, often rapidly, in time. The transmission delay of the packets will depend on the traffic load in the system and will thus also vary, often rapidly, in time. For a specific link, the transmission delay will depend on the number y of packets in line for transmission over the link. Packet losses may occur if transmission delays are too prolonged.
Telecom applications using packet transmission can be divided roughly into speech and data. In this case by xe2x80x9cspeechxe2x80x9d is meant spoken information between two end users in a dialog. Speech applications usually use circuit switched telecommunication systems for transmission, since these systems are developed to fulfil the stringent requirements on short delays. Nevertheless, packet data systems are expected to transfer more of the speech in the future. However, data is the major application for packet data networks at the present time. To compete with the telecommunication system on the transmission of speech, packet transmission systems must keep delays short.
Generally the demand for short delay is not as critical for data as for speech. Data, however, is more vulnerable to loss of data packets.
It has been suggested that Internet should support differentiated Quality of Service for separate services. This would result in speech transmission being given priority with respect to delay over the transmission of data when speech and data compete for common transmission resources. These discussions have been held within a group IETF (Internet Engenering Task Force).
A granted patent U.S. Pat. No. 4,538,259 is related to a communication system transmitting voice packets. The voice packets are transmitted through the network to a receiving node where they are reproduced into sound. To reproduce the sound the digitised voice packets have to be D/A converted at a certain rate. One problem is that variations in transmission delays cause the voice packets to arrive at the receiving node at different intervals. To adjust for the variations in delay packets are intentionally delayed slightly in the receiving node before being reproduced into sound. The object of U.S. Pat. No. 4,538,259 is to define an adequate intentionally delay in the receiving node. If it is to too long, the quality of the connection is negatively effected as the total delay increases. Speech packets may also be lost due to overflow in the receiver buffer. If, on the other hand, the delay in the receiver is made too short it will not suffice to compensate for the variations in the transmission delay. To achieve the object according to U.S. Pat. No. 4,538,259 the first voice packet is sent with priority, thereby having a more defined transmission time through the communication system.
The present invention is more closely related to a packet data service designated General Packet Data Service, which is hereafter referred simply as GPRS. GPRS is to be a standardised service for mobile communication system GSM and work has been going on for some years to this end within the European standardisation organisation ETSI. A GSM network will have a connection to other packet data networks, for instance networks using TCP/IP protocols and will receive data packets in the form of data frames for further transmission to a receiving mobile station. The received data frames are however to large to fit into the protocol of the radio link and are therefore split into data segments before being transmitted to the mobile station.
According to one proposal there is included a packet control unit for receiving data frames and splitting each frame into a sequence of data segments. A packet data link is connected from the packet control unit to at least one radio base station. The radio base station is provided with a number of radio links for packet transmission to a number of mobile stations. A data frame addressed to a certain mobile station is thus split into a sequence of data segments in the packet control unit. The sequence is then transmitted over the packet data link to the radio base station. The sequence is interleaved over the packet data link with other sequences of data segments to be sent from the packet control unit to the radio base station, i.e. segments of different sequences are mixed in the transmission flow. Segments received in the radio base station are then sent over the radio links. The radio channels are a scarce resource and there is a need to utilise them efficiently. The lower limit of the transmission delay within the GSM system is determined by the capacity of the radio link.
The architecture of a GSM-system supporting the GPRS service has not yet been settled.
It has recently been disclosed that also American operators intend to introduce the GPRS-service in the AMPS and IS-136 mobile radio systems.
The present invention addresses a problem of efficiently transmitting data segments over a first packet data link to be received in a first node in time for the first node to transmit the segments at predefined times over a second packet data link, when the first packet data link is also used for transmission of information packets having priority over the data segments and when the transmitted capacity of the first packet data link is limited.
The problem relates for example to a GSM-system that uses packet transmission between internal nodes, to provide for both a traditional circuit connected speech service and for packet data service handling applications such as Internet data services. The packet data service shall enable data frames to be received from a data network such as Internet and be transmitted to a designated mobile station. The traditional connected speech service shall provide for communications between a PCM coded link, i.e. a link traditionally used for a circuit switched connection, and a mobile station.
A data frame is received by a GSM network and divided into a sequence of data segments in the packet control unit such as to fit into the protocol of the radio link. PCM coded information, i.e. mainly speech, is continuously received by the GSM network and continuously coded into information packets, in the case of speech this is effected by speech transcoders. According to the example, the architecture of the GSM-system enables the data segments and the information packets to be transmitted to a radio base station on the same first packet data link, i.e. to the first node. On the first packet data link the flow of data segments and information packets compete for transmission capacity.
Information packets are given priority over data segments when transmitted over the first packet data link.
However, data segments also have to be delivered to the base station on time for transmission to the mobile station. When priority is given to the information packets there is a risk that no data segments will arrive at the base station at the times for transmission over the radio link.
The data segments corresponding to a sequence are consecutively transmitted over the radio link, i.e. a second packet data link, to the mobile station. The time for transmission of the segments is determined by the mapping of logical channels on the radio link, the synchronisation of the mobile stations and also on the need to utilise effectively the scarce resource of the radio link.
The present invention solves the problem, by a method in which the first data segments of a sequence derived from one data frame are transmitted over the first packet data link with the same priority as the information packets, thereby reducing the risk of the first data segments arriving too late at the first node. Instead, some of the first data segments probably arrive too early and are buffered until time for transmission over the second link. A subsequent transmitted data segment may thereafter be subjected to a longer delay than would otherwise be possible without causing a problem, due to the presence of a data segment that has already arrived in the first node and that is ready for transmission over the second data packet link at the predefined time.
The problem is also solved by a packet communication system comprising an interface with means to transform a received stream of information into a corresponding stream of information packets. The system also comprises a packet control unit for receiving a data frame, a first nod, a first packet data link connecting the interface and the packet control unit to the first nod. The packet control unit includes means for splitting a received data frame into a sequence of data segments. The packet communication system also comprises means for transmitting said stream of information packets and said sequence of data segments over the first packet data link with priority given to information packets and to some first data segments in the sequence of data segments.
The problem is also solved by a method in which data segments and information packets are transmitted over a first packet data link to a first node. Information packets are given priority on the first packet data link. Data segments received by the first node are each to be transmitted at a predefined time over a second packet data link. Data segments are buffered in the first node until the predefined times for transmission over the second packet data link. In the event of the number of data segments decreasing a threshold number, the first node sends a signal. In response to the signal some few data segments are sent with priority over the first packet data link. Thereby, filling of the buffer is speeded up.
According to one embodiment of the invention, the packet data system is a radio communication network with a PCM coded connection to the telecommunication network and a connection to a packet data network. Data frames received from the data network are divided into sequences of data segments. A stream of information received by the PCM coded connection is transformed into a corresponding stream of information packets. The data segments and the stream of information packets are transmitted over the first link to the radio base station, with priority given to the information packets and the first data segments of a sequence. Sequences of data segments and information packets are transmitted from the radio base station to a mobile station on separate packet data radio links.
An advantage with the present invention is that the risk of no data segment being available in the first node at the predefined time for transmission over the second packet data link is markedly reduced, just by giving the first few data segments of the sequence a higher priority.
Further advantages afforded by the invention will be apparent from the following analysis of a packet data radio communication system. There is a fundamental difference in transmission of a data frame received by a packet data network and a stream of information received by a telecommunication network. The data frame is divided into segments, that are transmitted to the first node and then to the mobile station. The data frame is not restored until all segments of the frame have been received in the mobile station, wherewith the information carried thereby can be retrieved. This implies that an inevitable delay is introduced to the data frame when received at the mobile station. The lenght of the delay is dependent on the capacity of the radio link for all the segments to be transmitted.
Speech packets and data segments are transmitted over separate radio links. Data segments are transmitted over the radio link in a consecutive order at defined times.
The fact that all data segments of the sequence are available in the packet control unit means that data segments can be sent in advance over the first packet data link and buffered in the radio base station until time for transmission on the radio link. As distinct from data segments, information packets may not be delayed in the radio base station. Any delay of information packets in the radio base station will have an affect on the total transmission delay.
The advantages afforded by the present invention will be fully apparent in the light of the above analysis. The main advantage resides in less danger of the first node, e.g. the radio base station, being devoid of data segments at the time for transmission over the second link, e.g. the radio link. If it were not for the invention, the risk of running out of segments would be greatest at the beginning of transmission of the sequence of segments, since no or only some segments are then are buffered in the first node. The risk of the radio base station running out of segments for transmission could, in theory, be reduced by increasing the traffic capacity of the first packet data link. However, to achieve the same risk reduction, the capacity of the first link would have to be greatly increased, at a corresponding cost. The solution according to the present invention is much cheaper to implement. The invention is easy to implement. In a system supporting differentiated Quality of Service the nodes already handles priorities and the invention can be implemented merely by adding priority information to some data segments.